Questions tagged [topology]
In mathematics, topology examines the properties of space (such as connectedness and compactness) that are preserved under continuous deformations, such as stretching and bending, but not tearing or gluing.
612
questions
2
votes
0answers
46 views
Is there any “realistic” metric of type $\mathrm{(A)dS}_2 \times \mathcal{T}_2$ in General Relativity?
After studying the Bertotti-Robinson metric, which describes a $\mathrm{AdS}_2 \times \mathcal{S}_2$ universe, I was wondering about other kind of closed topologies with holes, like $\mathrm{(A)dS}_2 \...
0
votes
2answers
65 views
Two particles at different points on a curved manifold
Stupid question, but why two particles at different
points on a curved manifold do not have any well-defined notion of relative velocity?
For instance n cosmology the light from distant galaxies
is ...
1
vote
1answer
49 views
Non-linear Perturbations of Minkowski Spacetime
I am reading some of the following paper on the bounded $L^2$ conjecture in general relativity where it mentions non-linear perturbations of the Minkowski metric in the context of quasilinear wave ...
1
vote
0answers
40 views
Proof of equivalence of variational principle and Euler-Lagrange equations on a manifold [closed]
Let M be some manifold, and TM the tangent bundle. Let $\gamma : [a,b] \to M$ be a smooth curve on M defined on an interval on $\mathbb{R}$. Let $J$ be another interval in $\mathbb{R}$ containing 0. A ...
2
votes
2answers
87 views
Does $\mathcal{M} = AdS_2 \otimes S_2$ makes any sense as a manifold?
I'm not a topologist or a group theorist and I need a clarification about some notations.
Consider the Bertotti-Robinson metric in General Relativity (relativity students should study this metric, by ...
1
vote
1answer
78 views
Orthochronous indefinite orthogonal group $O^+(m, n)$ form a group
My question is based on Qmechanic's answer here which proves that $O^+(m, 1)$ forms a group -- that if two Lorentz transformations have positive time-time co-ordinate, so does their product. The key ...
3
votes
2answers
56 views
Globally constant vector field in a curved spacetime
Is it possible to define a globally constant vector field in a curved spacetime, that is a vector field for which the covariant derivative vanishes along every world line? The vector field $V^{\mu}=0$ ...
0
votes
0answers
28 views
Harper-Hofstadter model in symmetric gauge
If I have l a square lattice, with the total flux = $\pi$, I can work in the symmetric gauge, which will have my vector potential be $A = \frac{\pi}{2}(-y,x)$. In a tight-binding model with Peirels ...
1
vote
1answer
87 views
Cylindrical universe cosmology in general relativity
Is there a compact cylindrical universe solution to the Einstein equation, with space homogeneity, without using "artificial" periodic boundaries? I'm expecting a metric of the following shape:
\...
0
votes
0answers
43 views
Electromagnetism on 3 torus
We all know Maxwell equations in 3+1 spacetime, where the "space" is $\mathbb{R}^3$ and time is $\mathbb{R}$. Moreover, it is easy to construct (using differential forms) the corresponding theory in a,...
1
vote
0answers
14 views
Understanding Skein relations
I'm just studying some concepts in the topology, but I cannot figure out totally how Skein relations work.
in the following I've one example:
which tries to relate Reidmeister II to the Skein ...
0
votes
1answer
56 views
How to know which topological invariant is in play?
I'm currently working on the Haldane model where I've worked through the math to find that when the condition
$$
\frac{M}{t_2} = 3 \sqrt{3} sin (\phi)
$$
is satisfied the gap closes, meaning there ...
1
vote
0answers
45 views
Does a topological charge always need to be an integer
Does a topological charge always need to be an integer, I see many papers where people talk about non-integer topological charges due to boundary conditions. According to the formula for the ...
2
votes
1answer
121 views
What if Newton's bucket had been a sphere?
My question involves a modification of Newton's bucket experiment. If a sphere filled (say) one-third or one-half with water is rotated very very fast, will the water eventually spread out across and ...
0
votes
0answers
14 views
What are the transformation equations for deviatoric planes?
What are the transformation equations $$r=r(x,y,c),$$ $$\phi=\phi(x,y,c)$$ for a Matsuoka-Nakai deviatoric plane? Variables $x,y$ are Cartesian coordinates, $r,\phi$ are "polar" coordinates, $c$ ...
7
votes
1answer
191 views
Does the Standard Model have texture defects?
In the standard classification of topological defects, in a theory with vacuum manifold $\mathcal{M}$,
$\pi_0(\mathcal{M})$ corresponds to domain walls,
$\pi_1(\mathcal{M})$ corresponds to strings/...
0
votes
1answer
37 views
In what sense do bifurcations concern change in quality?
I've heard such vague statements several times and also read:
Bifurcation theory is the mathematical study of changes in the qualitative or topological structure of a given family.
(From ...
0
votes
0answers
48 views
What makes a topological insulator topological?
I understand that a topological insulator is one with an insulating bulk and conducting surface but I don't understand why or how the topological part comes into it. All of the resources I've found ...
-1
votes
1answer
89 views
Does CMB rule out that the universe is infinite?
If the universe were infinite, the energy of the big bang would have been long dissipated, and very little or nothing would hit us. Does the fact that CMB still comes roughly the same from every ...
2
votes
1answer
102 views
Why is $\rm{Conf}(\mathbb{R}^{1,1}) = \rm{Diff}(S^1) \times \rm{Diff}(S^1)$ and not $ \rm{Diff}(\mathbb{R}) \times \rm{Diff}(\mathbb{R})$?
The Minkowski metric for $\mathbb{R}^{1,1}$ is
$$
ds^2 = dt^2 - dx^2 = du dv
$$
for coordinates
$$
u = t + x \hspace{1cm} v = t - x
$$
If you do any coordinate transformation that acts independently ...
1
vote
0answers
39 views
Spacetime manifolds of 1+1 d systems for writing TQFT partition functions
Are the spacetime manifolds of two unentangled systems disconnected?
This arises in the context of thinking of an operator whose expectation value we wish to take by writing this quantity in terms ...
3
votes
1answer
109 views
What's the meaning of “inequivalent quantizations”?
The notion "inequivalent quantizations" is regularly used when topological terms are discussed.
From what I've gathered so far, "inequivalent quantizations" means that there are different quantum ...
1
vote
0answers
32 views
What happens to large gauge transformations in gauges different from the temporal gauge?
There are already several questions regarding the meaning and definition of large gauge transformations.
Discussions of large gauge transformations typically only happen in the context of the ...
1
vote
0answers
56 views
Wave function as a section of a complex line bundle to do QM in polar coordinates
If you want to change the coordinates of a Wave function $\Psi$ in 2D QM from cartesian to polar coordinates in a naive way one encounters a problem, namely the (naively defined) radial momentum ...
1
vote
1answer
56 views
Is it mathematically impossible to incorporate the space curvature into the equations of motion and gravity? [duplicate]
Obviously, I haven't studied GR, I know no more than common knowledge. However, I'm wondering, is it impossible to develop a mathematical model based on flat space, in which the new equations of ...
2
votes
1answer
85 views
Lefschetz and Witten indices$.$
I couldn't help but notice a formal similarity between the Lefschetz index
$$
\mathrm{ind}(f)=\sum_k (-1)^k\operatorname{tr}(f_*|H_k)
$$
and the Witten index
$$
Z=\operatorname{tr}((-1)^Fe^{-\beta H})
...
asked May 30 at 22:21
AccidentalFourierTransform
26.5k14 gold badges75 silver badges135 bronze badges
1
vote
1answer
52 views
Is there a definition for a *geometric entropy*?
In statistical mechanics, entropy of a system is usually defined as a measure of the system's micro-state randomness, or as an averaged "surprise" of its micro-state:
\begin{equation}\tag{1}
S_{\text{...
1
vote
1answer
53 views
Understanding Anyonic Exchange
In the book of "Introduction To Topological Quantum Computation" by Jiannis K. Pachos, in chapter 5, it tries to explain anyonic exchange.
In the following, the $m$ and $e$ quasi-particles are ...
0
votes
2answers
73 views
Rigourous formalism of Hamiltonian mechanics on Manifolds
I'm looking for books / articles that provide rigorous formulations of Hamiltonian mechanics on Manifolds. I found the book "Global Formulations of Lagrangian and Hamiltonian Dynamics on Manifolds" [1]...
0
votes
1answer
44 views
Reference for topology for topological insulators
In the field of topological insulators
What topological space do they talk of?
Looking for some resources that sheds light on the topology part of topological insulator
2
votes
1answer
55 views
2-sheeted Riemann surface with 2 branch cuts and Torus
A 2-Sheeted Riemann surface, with 2 branch cuts has a genus 1. A ring torus also has a genus 1 (In fact, section 13.4 of John Terning's book, modern supersymmetry and dynamics and duality claims that ...
6
votes
2answers
85 views
Particle on a circle with magnetic flux$.$
I am trying to understand the model studied in 1905.09315 §2, to wit, a $0+1$ dimensional theory with target space $\mathbb S^1$ with non-trivial magnetic flux:
$$
\mathcal L=\frac12m\dot q^2-\frac{i}{...
asked May 25 at 23:06
AccidentalFourierTransform
26.5k14 gold badges75 silver badges135 bronze badges
4
votes
1answer
59 views
Pulling apart the atoms of a topological insulator
Consider a topological insulator. In order to destroy a topological phase, the band gap of the bulk system should close at some point (passing thru a conducting state), but if the atoms that make up ...
2
votes
0answers
45 views
Fluxes on a finite group $G$
So I've been studying about topological quantum computation and I have a few questions I haven't been able to solve. The first one is why fluxes take values on a finite group $G$? Does it have to do ...
3
votes
3answers
137 views
Rigorous procedure of gluing together two spacetimes
There seems to exist a procedure of "gluing two spacetimes together". In particular I've seem this mentioned in the context of gravitational collapse.
The examples I've seem where that of gluing ...
2
votes
0answers
21 views
What is the shape of the universe? [duplicate]
If it's flat then how a volume can be flat?
And I've read that it's actually not flat .....it's a "Poincaré dodecahedral space".
Any suggestions for books posts or articles are highly appreciated.
3
votes
0answers
54 views
Does the Einstein field equation uniquely determines the topology of spacetime? [duplicate]
I am trying to understand whether the Einstein field equation uniquely determines the topology of spacetime. As far as I know, given a metric, we can always find the induced topology. However, I was ...
1
vote
0answers
60 views
String topology in string theory
How do string topology, string field theory and topological strings interact? Does anybody see a global picture? By string topology I mean the TQFT based on the homology of the space of loops ...
0
votes
0answers
37 views
Can the shape of our Universe be a Mobius strip? [duplicate]
The Friedmann Equations describe three possibilities for the shape of our using General Relativity, I read in a book that the shape of our Universe is a 3-sphere such that in any direction if you ...
1
vote
0answers
33 views
Critical points of vector field with zeros in the magnitude
I am studying a vector field which has critical points (sources, sinks, saddle points and centers). The magnitude of the vector field goes to zero smoothly in these points, however. Contrast that to ...
1
vote
1answer
86 views
Berry phase: Spin in a magnetic field parameter space manifold
Canonical example for Abelian Bery phase is a spin in a magnetic filed, e.g.. Usually authors calculate spin eigenstates, conclude that they don't depend on B in spherical components and so deduce ...
2
votes
1answer
78 views
Topological theta-term as a background electric/magnetic field?
The topological $\theta$-term in the Schwinger model (1+1-dimensional QED) can be interpreted as a background electric field, as explained in Chapter 7.1.2 of Tong's lecture notes. The same holds true ...
2
votes
1answer
94 views
Theta-dependence of massive Schwinger model
I've read in Coleman's paper on the massive Schwinger model (and in other papers on the same topic, like this one) that the model's Hamiltonian contains a topological $\theta$-term. However, if I ...
1
vote
1answer
143 views
Black holes in p-adic gravity/ultra-metric metric field? [closed]
As a radically different to beyond standard general relativity, at least from the type of geometry it deals with:
Consider p-adic gravity and/or general relativity defined on certain ultra-metric ...
0
votes
0answers
9 views
What’s the topology of critical region?
Duhem said the aim of physics is natural classification. I think topology and geometry are a wonderful way to link analogous parts among different phenomena. Thus we can classify and predict facts. ...
5
votes
1answer
200 views
“Hidden” theta-term in Hamiltonian formulation of Yang-Mills theory
I've read in David Tong's lecture notes on gauge theory that the Hamiltonian of Yang-Mills theory does not depend on the angular parameter $\theta$, because it can be absorbed in the electric field:
$...
1
vote
0answers
43 views
Symmetry operators of a Bloch Hamiltonian
Consider a lattice with a 3 atom basis, e.g. the Lieb lattice, and some completely arbitrary on-site energies and hopping energies and phases between the different atoms. In momentum space we can ...
2
votes
1answer
39 views
Change in area on a 3-sphere bounded by a trajectory due to a differential change in trajectory
I have a 3 dimensional spherical topology, and I draw a curve onto the sphere labelled by $\vec{n}(\vec{r},t)$. The area bounded by the curve is termed the "Wess Zumino Action" (Hence my motivation to ...
2
votes
0answers
50 views
Hausdorff property in Minkowski spacetime
In the 4-dimensional Minkowski spacetime, for a given point $x = (x^0,x^1,x^2,x^3)$, its timelike future/past set is defined as,
$$ I^{\pm}(x) = \{y =(y^0,...,y^3) \in \mathbb{R}^4 : \eta_{\mu \nu}(y-...
0
votes
0answers
12 views
For the torus to rotate 180 degrees around the East-West symmetry axis, what happens?
(Suppose to ignore the deformed friction and torus when rotating)
